Paddy Soils in Tropical Asia: Part 5. Soil Fertility Evaluation

Abstract

Although there have been many studies intended to assess soil fertility, no established method for drawing quantitative conclusions relative to soil fertility is yet available. In this study the method of principal factor analysis was successfully applied to a set of 11 variables (TC, TN, NH_3-N, TP, Bray-P, HCl-P, Ex-(Ca+Mg), Ex-K, CEC, Available Silica, and Sand) routinely analyzed in the soil laboratory. Three mutually independent and clearly definable fertility component factors were extracted from these data on 410 tropical Asian paddy soils. They were named as inherent potentiality, organic matter-nitrogen status, and available phosphorus status. Inherent potentiality is closely related to the nature and amount of clay and the base status of soil. So it shows close relationship with the soil material classification set up in the previous study. The samples from each country or region were characterized by the scores of these three factors. Furthermore, based on the factor scores, a five-grade classification (very high, high, intermediate, low, very low) for each of the three fertility components was set up. The possibility of using these fertility components in a multiple regression analysis for crop yield prediction has also been suggested.